三峡库区支流库湾消落带土壤磷形态赋存特征及其释放风险

Distribution and Release Potential of Soil Phosphorus Fractions in Water-level Fluctuation Zone of the Tributary Bay,Three Gorges Reservoir

三峡库区消落带经历反复的淹水-落干循环影响,消落带土壤磷迁移转化过程加快,可能加剧支流库湾水体富营养化.采集了三峡库区腹心支流库湾典型消落带土壤,测定磷赋存形态与磷素饱和度(DPS)等,分析磷释放风险.结果表明,(1)消落带土壤ω[总磷(TP)]、ω[无机磷(IP)]和ω[有机磷(OP)]均值分别为771.80、485.33和166.30 mg·kg^(-1),IP和OP均以非活性形态磷为主.(2)消落带土壤形态磷的赋存格局受落干-淹水方式影响,Ex-P和NaHCO_(3)-Po含量显著高于对照土壤,Fe-P、HCl-Po和Fulvic-Po含量沿高程下降而显著降低(P<0.05),反复的干湿交替促进了消落带土壤活性磷的生成和中等活性磷的释放和积累.(3)消落带土壤生物ω[有效磷(Bio-P)]为49.19~148.78 mg·kg^(-1),占TP的质量分数为7.71%~24.78%,磷素饱和度(DPS)为5.85%~22.00%.目前,支流库湾消落带土壤整体磷释放风险较低,170 m高程土壤需要重点关注.Fe-P、HCl-Po和Fulvic-Po在消落带土壤磷释放过程中贡献较大,pH升高会促进Fe-P的释放,碱性磷酸酶(ALP)是有机磷转化的重要参与者,有机质(OM)是有机磷的主要来源.

After repeated wetting-drying cycles,the migration and transformation of phosphorus in the water-level fluctuation zone(WLFZ)are accelerated,and the eutrophication of tributary bays in the reservoir becomes increasingly serious.Soils in the WLFZ of a typical tributary of the Three Gorges Reservoir were collected,and then phosphorus forms and the degree of phosphorus saturation(DPS)were determined to analyze the phosphorus release potential.The results showed that,①the average contents of total phosphorus(TP),inorganic phosphorus(IP),and organic phosphorus(OP)of soils in the WLFZ were 771.80,485.33,and 166.30 mg·kg^(-1),respectively.The non-labile IP and OP were the dominate speciation of IP and OP,respectively.②The distribution of P forms of soils in the WLFZ was affected by wetting-drying cycle.The contents of Ex-P and NaHCO_(3)-Po of soils in the WLFZ were significantly higher than those in the contrasted soils,whereas the contents of Fe-P,HCl-Po,and Fulvic-Po decreased significantly along the elevation(P<0.05).The alternative wetting-drying cycle promoted the generation of labile P and the release and accumulation of moderately labile P of soils in the WLFZ.③The content and proportion of bioavailable phosphorus(Bio-P)of soils in the WLFZ were in the range of 49.19-148.78 mg·kg^(-1)and 7.17%-24.78%,and the degree of phosphorus sorption(DPS)was in the range of 5.85%-22.00%.At present,the phosphorus release risk of soils in the WLFZ was low.The soil at 170 m elevation requires further attention.Fe-P,HCl-Po,and Fulvic-Po contributed significantly to phosphorus release.The increase in pH promoted the release of Fe-P.Alkaline phosphomonoesterase(ALP)was an important participant in the transformation of OP.Additionally,organic matter(OM)was the main source of OP.